Atoms are first excited and then ionized by two different laser pulgeg, respectively. When the energy per pulse of the ionizing laser is near 1J/cm2, the ionization is saturated. By measuring the relative number of ionized atoms versus the ionizing laser energy, we can easily obtain the photoionization cross section for the excited state of the atoms. The ionizing laser pulse is delayed until the exciting laser pulse is stopped. It aims to eliminate the contribution of the ionization signal produced by the exciting laser and to avoid the Stark shift produced by the ionizing lager. The pliotoionization cross section for Cs (72P3/2) at 532.0 nm has also been measured. The measured value is σI=6.5×10-18 cm3, which is close to Manson's calculation.